GB 2 233 089 discloses a method and apparatus for monitoring the aggregation of particles suspended in a liquid, in which a sample of the liquid is subjected to ultrasound to promote aggregation and possible agglutination of particles, and then the particles are allowed to settle onto a meniscus of the sample. A visual inspection of the particles once settled on the meniscus enables a determination of whether an agglutination reaction has occurred: agglutinated cells lie in clumps distributed over the meniscus, whereas clumps of non-agglutinated particles dissociate and form a ring around the edge of the meniscus.
The method and apparatus disclosed in GB 2 233 089 is particularly applicable to the detection of Hepatitis B virus, a reaction mixture being formed of a serum sample plus a suspension of appropriate erythrocytes coated with antibody to Hepatitis B surface antigen. Viral agglutination of the erythrocytes gives a positive test reaction.
In GB 2 233 089, ultrasound is coupled via a reservoir into the bottom of a vertical capillary tube containing the sample. The arrangement is not suited to multiple-sample testing because the reservoir, in which the capillary tube stands, must be washed out and refilled for each test; also continuous movement of successive samples through the capillary tube is impractical because the ultrasonic transducer is positioned across one end of the capillary tube.